[Structure of glyceraldehyde-3-phosphate dehydrogenase from rat muscle. Localization of arginine residues modified by 2,3-butanedione]. / Issledovanie struktury glitseral'degid-3-fosfatdegidrogenazy iz myshts krysy. Lokalizatsiia argininovykh ostatkov, modifitsiruemykh 2,3-butandionom.

Modification of rat skeletal muscle hologlyceraldehyde 3-phosphate dehydrogenase by [2,3-14C]butanedione was carried out. The conditions for obtaining preparative amounts of the modified protein and for the maintenance of the modification product stability at various steps of treatment were elaborated. Two radioactive peptides containing modified arginine residues were isolated from the trypsin hydrolysate of the enzyme modified by [2,3-14C] butanedione and oxidizied by performic acid, and their amino acid sequence was established. The data obtained suggest that the essential arginine residue occupies position 134 in the primary structure of the rat muscle enzyme.

[Serratia marcescens endonuclease. Properties of the enzyme]. / Endonukleaza Serratia marcescens. Kharakteristika fermenta.

Some physico-chemical properties of endonuclease (EC 3.1.4.9) from Serratia marcescens were studied and the amino acid composition of the enzyme was determined. The protein molecule was shown to contain one SH-group and one S-S-bond, which renders it different from the well studied nuclease (EC 3.1.4.7) from Staph. pyogenes. The conditions for reconstitution of the S-S-bond by dithioerythritol for quantitative estimation of cysteine residues of the endonuclease molecule were selected. The N-terminal amino acid was found to be threonine. The UV spectra for the enzyme are typical for proteins; A 0,1% 1cm,280nm is 1.46, epsilon 25 degrees 280nm,pH7,4 is 47292 M-1 cm-1. The sedimentation coefficient in phosphate buffer sW, 20 degrees is 3.4 S, pI is 6.5 and 7.5.

[Structural studies on D-glyceraldehyde-3-phosphate dehydrogenase from rat skeletal muscle]. / Issledovanie struktury D-glitseral'degid-3-fosfatdegidrogenazy iz skeletnykh myshts krysy

The amino acid composition of glyceraldehyde-3-phosphate dehydrogenase isolated from rat skeletal muscle was determined. Tryptic peptide maps of the carboxymethylated protein were compared with those of the corresponding derivative of the rabbit muscle dehydrogenase. Evidence from the amino acid analysis, N-terminal amino acid and the position of the peptides in two-dimensional chromatography-electrophoresis suggests a high degree of homology between the two enzymes. However, the rat muscle glyceraldehyde-3-phosphate dehydrogenase is characterised by a markedly lower histidine content. Some differences are also revealed in the peptide maps of the rat and rabbit dehydrogenases. Four cysteine residues per subunit of rat apoenzyme may be carboxymethylated in the absence of denaturing agents (pH 8,4 75 min). Two of them are modified at pH8,0 within 30 min and are both found in the peptide, which has been demonstrated to contain the most reactive cysteine residue. This suggests cysteine residue N 153 to be the second in order of reactivity towards iodacetate. No difference in the accessibility of SH groups to iodacetic acid has been found between apoenzyme samples incubated in 0,15 M NaCl at 20 degrees and 4 degrees respectively. This indicates that enzyme inactivation caused by dissociation which occurs at low temperature brings about no measurable alterations in the SH group reactivity as compared to that observed at 20 degrees.